Titanium Additive Manufacturing Evolves Incrementally To Achieve ‘Qualification’ of Global Aerospace Industry By Bill Bihlman
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ost people are familiar with the concept of 3D printing or additive manufacturing (AM) as it pertains to aerospace manufacturing. What most do not understand, however, is its level of maturity and the implications for their respective businesses. Titanium castings and smaller machined titanium parts are particularly at risk. Yet the timeline might not be as aggressive as many believe, or hope. AM has evolved substantially since its genesis in the mid-1980s. Nearly simultaneously, Scott Crump, Chuck Hull, and Carl Deckard were experimenting with various ontologies or “modalities” of an additive process. These involved fused deposition modeling, stereolithography, and selected laser sintering, respectively. (ASTM has subsequently established the taxonomy: Material Extrusion, Vat Photopolymerization, and Powder Bed Fusion, respectively.) Initially, this new manufacturing paradigm was limited to rapid prototyping (as evidenced by the name of the largest AM conference in the United States, RAPID, established by the Society of Manufacturing Engineers in 1990). Nowadays, AM is being used for some serialized production metal parts for aircraft and turbine engines. One of the more compelling use cases is the GE Catalyst engine. The company boasts of printing 35 percent of its gas turbine, replacing over 850 castings with only a dozen printed parts, likely using Ti-6Al4V. Perhaps even more intriguing is printing titanium-aluminide (Ti-AL) 14
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low-pressure turbine blades for the b) produce high near-net shapes with GEnx engine. smooth surfaces. Regardless of the Most of the examples of AM modality, processing titanium (and in aerospace involve one of two aluminum) requires shielding. This modalities: powder-bed fusion (PBF) usually involves gas, such as argon, or directed-energy deposition (DED). to protect the melt pool from oxygen Powder-bed fusion uses an energy contamination. source (e.g. laser) to melt a thin layer It is believed that PBF represents of metal powder. These particles are at least 70 percent of the metal tiny—a fraction of the thickness of a parts printed for aerospace, when human hair. A mechanical including commercial “recoater” spreads layerspace applications. upon-layer of powder after Furthermore, it each passing melt cycle. is estimated that Parts are limited to the titanium alloys size of the build chamber, represent roughly with dimensions often 25 percent of the referenced in millimeters. total (see Figure 1). Larger parts require Note that titaniumthousands of layers and powder additive tens of hours to build. The manufactured parts benefit is that designs can are also extensively Bill Bihlman is founder of include nested features used for medical Aerolytics (website: www. or “conformal” cooling applications due to aerolyticsllc.com channels. In many cases, its biocompatibility. additive manufactured In either case, the parts have such dominant titanium sophisticated geometry and features alloy is Ti-6Al-4V. (e.g. internal lattice) that they cannot be created conventionally. The other common modality for aerospace is directed-energy deposition. This uses either wire or powder as a feedstock. In both cases, the feedstock is fed through a nozzle and melted to form a part as the nozzle traces a pattern of the future part. The advantages of DED are the larger build envelope and higher rates of deposition. The disadvantages are the inability to: a) create complex, Figure 1: Rough estimate of powder demand detailed parts compared to PBF, for aerospace PBF parts (source: Aerolytics) including “thin-wall” sections; and,
